Cost-effective recycling of materials, such as glass, plastics, and metals, has become an increasingly important issue to many businesses because of ever-increasing legislative mandates at the federal, state, and local levels and the associated cost of complying therewith. In a recycling process, an entity such as a material recovery facility (MRF) can face several significant challenges concerning increasing and/or optimizing the amount of recyclable materials recovered during processing, and decreasing operational costs such as labor costs.
A MRF generally serves as a drop-off and gross-sorting (and limited processing) point for recycled materials, so that sorted recycled materials can be transported, for example, to a customer of the recycled material for subsequent processing. Recyclable materials generally enter a MRF either in a single stream or dual stream. A single stream consists of a mixture of glass, plastics, and/or metals (collectively referred to herein as “commingled containers”), old news print (ONP) (e.g., newspaper and newspaper inserts), old corrugated paper (OCC), old telephone directories (OTD), old magazines (OMG), junk mail and/or office paper (collectively referred to herein as “fiber material”). A dual stream MRF consists of a commingled container stream and a fiber material stream. While traditional MRFs typically utilize a dual stream configuration, the desire to reduce labor and other operational costs has been an impetus behind the trend toward single stream MRFs.
A gross sort involves separating material by type. For example, glass, plastic, aluminum, fiber, etc. can each be physically separated from each other. In the case of glass, a conventional MRF typically sorts glass by size and color, each of which incurs a labor cost, can cause substantial wear and tear on machinery and equipment, and generally results in higher maintenance costs and lower profit margins.
Regarding size, much of the glass that enters a MRF is not in the form of whole containers. Instead, containers are typically broken, often into numerous pieces of widely varying sizes, which can complicate and increase the cost associated with sorting glass at a conventional MRF. Pieces of mixed color (e.g., flint, amber, green) glass smaller than approximately 2.5 inches are referred to as mixed cullet or residue (hereinafter mixed cullet). Currently, the economics of glass recycling is such that it is profitable (or more profitable) for pieces of glass approximately 2.5 inches or larger to be cleaned and processed for recycling, as it is generally too difficult and expensive to sort, clean and otherwise process mixed cullet.
Mixed cullet is thus typically either used in aggregate form as a landfill cover material, or is further processed, at an additional cost, so that it can be used, for example, as a paving material such as glasphalt (a highway paving material in which recovered ground glass replaces some of the gravel in asphalt) and/or aggregate (material such as glass, sand or small stones mixed with a binder such as cement to produce mortars and concrete).
U.S. Pat. No. 5,588,598, entitled “Commingled Recyclables Recovery and Recycling Process and Related Apparatuses,” which is incorporated herein by reference, describes how glass unsuitable for recovery is introduced into a trommel processing loop which substantially removes contaminants, and reduces the glass to a particulate. However, processing the mixed cullet as landfill or as a paving material is generally less profitable than processing a same volume of glass that does not include mixed cullet for subsequent sale to a beneficiator and/or a glass plant.
In addition, sorting glass by color (e.g., into flint, amber, and green components) also poses challenges to a MRF. Color sorting for both mixed cullet and pieces of glass greater than approximately 2.5 inches in size is desirable for use in conventional glassmaking techniques. U.S. Pat. No. 5,485,925, entitled “System and Method for Separating Recycled Debris,” which is incorporated herein by reference, discusses several initial screening methods, including manual sorting. European patent EP0439674, entitled, “Device for Sorting Waste,” which is incorporated herein by reference, describes the use of robotic sorters. However, U.S. Pat. No. 5,485,925 and European Pat. No. EP0439674 do not address the issue of recovering mixed cullet.
Further, because there are inherent limitations associated with conventional MRF processing techniques, such as manual sorting, that are used to sort glass by color, contaminants will not be completely removed from the glass stream. Contaminants that remain in the glass stream may cause quality and safety issues in finished glass products. For example, ceramic impurities remaining in the glass stream may adversely affect the glass recycling and manufacturing process, as well as the structural integrity of the finished glass product. Thus, there is a need to improve the cleanliness of glass recovered from the recycling process.
Finally, due to the implementation of single stream collection methods, glass is being broken at a substantially higher rate throughout the collection process. As a result, a much higher percentage of mixed cullet is being produced, with much of the increased production not being able to be recycled using conventional MRF processing techniques.
We have thus determined that it would be generally beneficial to increase and/or improve the profitability associated with recycling glass. In particular, we have determined that it would be beneficial to be able to improve the profitability associated with recycling mixed cullet. We have determined that it would be beneficial to increase the yield of glass recovered from the recycling process. We have further determined that it would be beneficial to be able recycle glass without having to sort the glass by size and/or color. In addition, we have determined that eliminating the need to sort glass by size and color advantageously decreases the labor, equipment, and equipment maintenance costs associated with recycling glass. In addition, we have determined that it would be generally be beneficial to be able to increase the cleanliness of the mixed cullet recovered from the recycling process, such as by removing ceramics prior to transporting the mixed cullet to a beneficiator or glass plant.
We have discovered new and useful ways of utilizing, for example, one or more optical sorters in connection with a single stream MRF. In particular, we have discovered that the use of optical sorters can, for example, reduce labor costs, provide for increased automation and thereby improve efficiency of sorting, increase the quality of sorted material, and generally increase profitability by increasing recovery rates. We have also discovered that there is a need to utilize one or more optical sorters to collect, track, and process constituent data of at least some recyclable material in a manner that, for example, enables MRF operations to be modified in a manner that facilitates improved processing efficacy and profitability.